A distributed digital communication network typically includes a multiplicity of nodes interconnected by transmission links. At least some nodes are typically accessible to at least some other nodes only by multiple links. In addition, at least some links typically not only have different transmission characteristics, particularly in the sense of transmission bandwidth, transmission delay, bit error rate, and the availability or unavailability of encryption but also have different transmission costs.
In transmitting a message between two nodes in such a distributed digital transmission network, it is normally advantageous to select the route entailing the lowest transmission costs before setting it up. In the past, an algorithm called the Dijkstra Shortest Path First (SPF) algorithm has been widely used for such selections. The SPF algorithm is disclosed, for example, at pages 586 through 589 of the second edition of "Data Structures Using Pascal," by Aaron Tennenbaum and Moshe Augenstein, which was published in 1986 by Prentice-Hall. Specifically, the SPF algorithm includes two separate and distinct steps. In the first step, the transmission distance between an originating node and each other node in the network is calculated. The shortest transmission distance to each potential destination node is saved in the originating node's memory. When a route is needed for transmitting a message to a particular destination node, the second step of the SPF algorithm determines a route with shortest transmission distance to the source node by tracing backwards from the destination node. Unfortunately, the selected route will not necessarily meet all transmission requirements of the message for which the route is being set up. If the selected route fails to meet all transmission requirements of the message, an entirely new calculation is necessary and establishment of a working route will be delayed. Because transmission distance may not be the only factor affecting cost, the selected route may also not really be the least cost route.